The charity at the centre of the rescue of three women from 30 years of alleged slavery in London has been inundated with calls for help from other victims.

Aneeta Prem, founder of the Freedom Charity, said her helpline had received calls from individuals saying they were being held in servitude since news broke of the women's case.

Police said a couple bailed on Thursday had been arrested on suspicion of immigration offences as well as in connection with the investigation into slavery and domestic servitude.

The couple had previously been arrested in the 1970s, according to Scotland Yard.

Police say the three women were not trafficked, and they are not looking for any more suspects or victims.

Prem said of the case: "This has to be a story of hope. A number of calls are coming through from people who have seen the media coverage and want to tell us they are in the same situation."

She said the three women who were rescued from a house in Lambeth, south London, last month were being given specialist care, had been seen by doctors and psychologists and were being continually supported. "They are taking things very slowly," she said.

The eldest woman – the 69-year-old Malaysian – was in this country and joined the suspects at their home more than 30 years ago. The 57-year-old Irish woman was also allegedly held by the suspects, a couple both aged 67, the Guardian understands.

The youngest woman, 30, may have been born in the house and allegedly had no contact with the outside world.

Met detectives are trying to discover the "invisible handcuffs" which held three women inside a house for so long.

Commander Steve Rodhouse said the women's case was like nothing the police had come across before.

"We are trying to find out what were the invisible handcuffs that were used to exert such control over these women. We are uncovering a complicated and disturbing picture of emotional control over many years, brainwashing is the term you could use."

The woman also received beatings, said Detective Inspector Kevin Hyland, head of the inquiry.

Police delayed the arrest so they could work sensitively with the victims to establish the facts of the case.

It emerged that the two suspects had been arrested by the force in the 1970s.

Rodhouse refused to reveal whether the couple had a criminal record.

"The people at the heart of this investigation probably have come into contact with public services including our own. We need to examine this more fully," he said.

The police are not investigating the women being trafficked. But the suspects are believed to have committed immigration offences.

Police and campaigners said the case highlighted a growing problem of slavery in Britain. Prem told ITV's Daybreak programme on Friday that she had met the three women on Thursday.

"They're quite traumatised … but they're very relieved to be out."

The women were rescued after the Irish woman saw Prem on a TV documentary and contacted the charity for help. Prem said it would be "a very long journey" to rehabilitate the women.

She said: "It's going to be a difficult process. Bear in mind these ladies have left with absolutely nothing at all. The charity is going to have to try to help and support them through this difficult journey."

The Irish woman contacted Freedom on 18 October to say she had been held against her will for more than 30 years, and that two others were held with her. She and the British woman met charity workers and police on 25 October before returning to the address and rescuing the Malaysian woman.

After a "traumatic and very difficult" first call to Freedom staff, Prem said she arranged a single point of contact for the women and began "secret negotiations" to bring them out.

She said: "We did it in a very slow way to gain their trust, because after 30 years of people being held in very difficult circumstances, one of the things we didn't want to do was to add any more trauma."

Hyland said 55 bags of evidence were removed from the house.

The couple have been questioned over false imprisonment, domestic servitude and offences against the person. Their passports have been seized and they have bail conditions that prevent them returning to the address where the women were held.